The following invention relates to magnetic discs and, in particular, a device for improving the yield of magnetic discs coated with carbon using ion beam deposition.
Magnetic discs are generally used for storing data in magnetizable form. Typically, one or more disks are rotated on a central axis in combination with data transducing heads positioned in close proximity to the recording surfaces of the disks and moved generally radially with respect thereto. Magnetic disks are usually housed in a magnetic disk unit in a stationary state with a magnetic head having a specific load elastically in contact with and pressed against the surface of the disk.
It is desirable during reading and recording operations to maintain each transducing head as close to the corresponding recording surface as possible, i.e., to minimize the flying height of the head. This is particularly important when the areal recording density of the magnetic media increases. (The areal density (Mbits/in.sup.2) is the recording density per unit area and is equal to the track density (TPI) in terms of tracks per inch times (.times.) the linear density (BPI) in terms of bits per inch). Thus, a smooth recording surface is preferred, as well as a smooth opposing surface of the associated transducing head, so that the head and the disk can be positioned in close proximity to each other.
A typical magnetic disc is comprised of a substrate, typically an aluminum (Al)-base alloy, such as an aluminum-magnesium (Al--Mg) alloy, plated with a layer of amorphous nickel-phosphorous (NiP). Deposited on the substrate is a chromium (Cr) underlayer, a cobalt (Co)-base alloy magnetic layer, a protective carbon overcoat and a lubricant topcoat. The Cr underlayer, the Co-base alloy magnetic layer and the protective carbon overcoat are typically deposited using sputtering techniques.
The efficiency of the magnetic disc manufacturing process is determined by the yield performance of the process. The yield performance is comprised of two factors: glide yield and certification yield. The glide yield is determined by flying a head over the disc surface at a predetermined height, typically below 1 microinch. If the head "hits" the disc surface, the disc is rejected. Discs that pass the glide test are then subjected to a certification test in which magnetic information is written to the disc. The information is then read from the disc and compared to the previously written information. If the comparison fails beyond an acceptable threshold, then the disc has failed the certification test and is rejected. Certification defects are caused by a number of factors including substrate defects, blisters from ineffective cleaning, or environmental contaminants on the disc surface before the sputter deposition of the chromium and magnetic layers.
The process of depositing a carbon film on a magnetic disc traditionally involved sputtering a carbon target with a mixture of argon and hydrogen gas. Recently, an emerging technology called ion beam deposition has been used to deposit carbon film on a magnetic disc.
Referring now to FIG. 1, there is shown an Intevac MDP 250 deposition machine 1 used for ion beam deposition. Deposition machine 1 includes a turbomolecular pump 3 placed on a process chamber 9. Process chamber 9 is mounted on a process station 5. Inside process station 5 is a carousel (not shown) that includes a disc pedestal on which a disc to be carbon coated is placed. An ion source 7, typically operating on a feed of hydrocarbon and argon gas, is introduced into process chamber 9.
In operation, the disc is positioned in process chamber 9. Ion source 7, which generates an ion beam consisting of positively charged ions of argon and hydrocarbon, is propelled towards the disc by the pumping pressure of turbomolecular pump 3 and coats the disc. The ion beam deposition process requires high gas flows (to ion source 7) and low pressures (created by turbomolecular pump 3) in order to deposit at a rate sufficient for manufacturing throughput. This combination necessitates high pumping capacity in process chamber 9.
A drawback of the prior art ion deposition process is that some residual ions and neutrals also deposit onto the vanes and stators of turbomolecular pump 3. After a sufficient amount of deposition onto the vanes and stators, the deposits flake off and fall into process chamber 9. These deposits may cause the disc to become contaminated thereby greatly reducing the yield performance of the ion deposition process.